Vehicular tires are sometimes desired to have rubber treads having a beneficially reduced hysteresis together with acceptable abrasion resistance physical property. Acceptable tear resistance physical property may also be desired.
Tires, such as truck tires intended for heavy duty performance, are sometimes desired to have treads of rubber composition of such properties.
Reduced rubber hysteresis property for a tire tread rubber composition is often desired to promote reduced internal heat generation within the tread during tire service and to promote reduced tire rolling resistance of the tire itself leading to reduced vehicular energy expenditure with an accompanying reduction in vehicular fuel consumption (beneficial increase in fuel economy) for the associated vehicle. Predictive beneficially reduced hysteresis for the tread rubber composition is normally evidenced by at least one of increased rebound physical property and decreased tangent delta (tan delta) physical property for the cured rubber composition.
An increased stiffness property for a tire tread rubber composition is also often desired to promote tire handling characteristics for the tire. Predictive beneficially increased stiffness of the tire tread rubber composition is normally evidenced, for example, by an increased storage modulus (G′) property of the cured rubber composition at low strains (low dynamic test elongations).
For this invention, a tire tread rubber composition is provided which contains reinforcing filler comprised primarily of rubber reinforcing carbon black where the rubber reinforcing carbon black is comprised primarily of rubber reinforcing carbon black having an oxidized surface.
The use of surface oxidized carbon black in place of a significant portion of the rubber reinforcing carbon black (carbon black which is not such oxidized carbon black) has been observed to provide a rubber composition having a significant and beneficially reduced hysteresis property, which may be desirable for a tire tread composition (e.g. lower tan delta physical property), to thereby promote a reduction in internal heat generation during tire service. However, it has also been observed that a stiffness property of the rubber composition may be reduced, often to a considerable extent as evidenced by a reduction in its storage modulus G′. Further, a reduction in abrasion resistance of the rubber composition may be experienced which is normally undesirable for a tread rubber composition.
An additional significant observed deficiency by use of the surface oxidized carbon black in place of a significant portion of the rubber reinforcing carbon black in a rubber composition has been a significant increase in its electrical resistivity (reduction in electrical conductivity) apparently resulting from the oxidized surface of the carbon black. In this manner, an undesirable buildup of electrical energy within the tire is promoted by a resistance to transmission of internally generated electrical energy within the tire through the tire tread for its emission from the tire tread surface to the ground.
A challenge is therefore undertaken to evaluate promoting an increase in the rubber composition stiffness or the rubber composition abrasion resistance, as well as promoting a reduction of its electrical resistivity (increasing its electrical conductivity), particularly for a tire tread rubber composition where a significant portion of its carbon black reinforcing filler is comprised of surface oxidized carbon black.
To meet such significant challenge, it is desired to evaluate providing an additive comprised of an amide of formula (I) for such rubber composition:
wherein R1 is an alkyl radical comprised of from 12 to 36 carbon atoms, an alkenyl radical comprised of from 12 to 36 carbon atoms or alkadienyl radical comprised of from 12 to 36 carbon atoms.
In the description of this invention, the terms “compounded” rubber compositions and “compounds” are used to refer to rubber compositions which have been compounded, or blended, with appropriate rubber compounding ingredients. The terms “rubber” and “elastomer” may be used interchangeably unless otherwise indicated. The amounts of materials are usually expressed in parts of material per 100 parts of rubber by weight (phr).